The present invention relates generally to methods of making nonwoven fabrics, and more particularly, to a method of manufacturing a nonwoven fabric exhibiting improved physical characteristics while exhibiting improved three-dimensional image, permitting use of the fabric in a wide variety of consumer applications.
The production of conventional textile fabrics is known to be a complex, multi-step process. The production of fabrics from staple fibers begins with the carding process whereby the fibers are opened and aligned into a feedstock referred to in the art as xe2x80x9csliverxe2x80x9d. Several strands of sliver are then drawn multiple times on a drawing frames to; further align the fibers, blend, improve uniformity and reduce the sliver""s diameter. The drawn sliver is then fed into a roving frame to produce roving by further reducing its diameter as well as imparting a slight false twist. The roving is then fed into the spinning frame where it is spun into yarn. The yarns are next placed onto a winder where they are transferred into larger packages. The yarn is then ready to be used to create a fabric.
For a woven fabric, the yarns are designated for specific use as warp or fill yarns. The fill yarns (which run on the y-axis and are known as picks) are taken straight to the loom for weaving. The warp yarns (which run on the x-axis and are known as ends) must be further processed. The large packages of yarns are placed onto a warper frame and are wound onto a section beam were they are aligned parallel to each other. The section beam is then fed into a slasher where a size is applied to the yarns to make them stiffer and more abrasion resistant, which is required to withstand the weaving process. The yarns are wound onto a loom beam as they exit the slasher, which is then mounted onto the back of the loom. The warp yarns are threaded through the needles of the loom, which raises and lowers the individual yarns as the filling yarns are interested perpendicular in an interlacing pattern thus weaving the yarns into a fabric. Once the fabric has been woven, it is necessary for it to go through a scouring process to remove the size from the warp yarns before it can be dyed or finished. Currently, commercial high-speed looms operate at a speed of 1000 to 1500 picks per minute, where a pick is the insertion of the filling yarn across the entire width of the fabric. Sheeting and bedding fabrics are typically counts of 80xc3x9780 to 200xc3x97200, being the ends per inch and picks per inch, respectively. The speed of weaving is determined by how quickly the filling yarns are interlaced into the warp yarns, therefore looms creating bedding fabrics are generally capable of production speeds of 5 inches to 18.75 inches per minute.
In contrast, the production of nonwoven fabrics from staple fibers is known to be more efficient than traditional textile processes, as the fabrics are produced directly from the carding process.
Nonwoven fabrics are suitable for use in a wide variety of applications where the efficiency with which the fabrics can be manufactured provides a significant economic advantage for these fabrics versus traditional textiles. However, nonwoven fabrics have commonly been disadvantaged when fabric properties are compared to conventional textiles, particularly in terms of resistance to elongation, in applications where both transverse and co-linear stresses are encountered. Hydroentangled fabrics have been developed with improved properties, by the formation of complex composite structures in order to provide a necessary level of fabric integrity. Subsequent to entanglement, fabric durability has been further enhanced by the application of binder compositions and/or by thermal stabilization of the entangled fibrous matrix.
Nonwoven composite structures typically improve physical properties, such as elongation, by way of incorporation of a support layer or scrim. The support layer material can comprise an array of polymers, such as polyolefins, polyesters, polyurethanes, polyamides, and combinations thereof, and take the form of a film, fibrous sheeting, or grid-like meshes. Metal screens, fiberglass, and vegetable fibers are also utilized as support layers. The support layer is commonly incorporated either by mechanical or chemical means to provide reinforcement to the composite fabric. Reinforcement layers, also referred to as a xe2x80x9cscrimxe2x80x9d material, are described in detail in U.S. Pat. No. 4,636,419, which is hereby incorporated by reference. The use of scrim material, more particularly, a spunbond scrim material is known to those skilled in the art.
Spunbond material comprises continuous filaments typically formed by extrusion of thermoplastic resins through a spinneret assembly, creating a plurality of continuous thermoplastic filaments. The filaments are then quenched and drawn, and collected to form a nonwoven web. Spunbond materials have relatively high resistance to elongation and perform well as a reinforcing layer or scrim. U.S. Pat. No. 3,485,706 to Evans, et al., which is hereby incorporated by reference, discloses a continuous filament web with an initial random staple fiber batt mechanically attached via hydroentanglement, then a second random staple fiber batt is attached to the continuous filament web, again, by hydroentanglement. A continuous filament web is also utilized in U.S. Pat. Nos. 5,144,729; 5,187,005; and 4,190,695. These patents include a continuous filament web for reinforcement purposes or to reduce elongation properties of the composite.
More recently, hydroentanglement techniques have been developed which impart images or patterns to the entangled fabric by effecting hydroentanglement on three-dimensional image transfer devices. Such three-dimensional image transfer devices are disclosed in U.S. Pat. No. 5,098,764, which is hereby incorporated by reference; with the use of such image transfer devices being desirable for providing a fabric with enhanced physical properties as well as an aesthetically pleasing appearance.
For specific applications, a three-dimensionally imaged nonwoven fabric must exhibit a combination of specific physical characteristics. For example, when such fabrics are used in the formation of cleansing or dusting wipes, the fabric must exhibit sufficient durability to withstand application upon abrasive surfaces and yet exhibit a pronounced three-dimensional pattern so as to capture and retain particulates (application filed separately). Further, three-dimensionally imaged nonwoven fabrics used in home, medical and hygiene applications require sufficient resistance to elongation so as to resist deformation of the image when the fabric is converted into a final end-use article and when used in the final application.
Notwithstanding various attempts in the prior art to develop a three-dimensionally imaged nonwoven fabric acceptable for home, medical and hygiene applications, a need continues to exist for a nonwoven fabric which provides a pronounced image, as well as the requisite mechanical characteristics.
The present invention is directed to a method of forming a nonwoven fabric, which exhibits a pronounced three-dimensional image that is durable to both converting and end-use application. In particular, the present invention contemplates that a fabric is formed from a precursor web comprising at least one support layer or scrim, which when subjected to hydroentanglement on a moveable imaging surface of a three-dimensional image transfer device, an enhanced product is achieved. By formation in this fashion, hydroentanglement of the precursor web results in a more pronounced three-dimensional image; an image that is durable to abrasion and distortion due to elongation.
In accordance with the present invention, a method of making a nonwoven fabric embodying the present invention includes the steps of providing a precursor web comprising a fibrous matrix. While use of staple length fibers is typical, the fibrous matrix may comprise substantially continuous filaments. In a particularly preferred form, the fibrous matrix comprises staple length fibers, which are carded and cross-lapped to form a precursor web. In one embodiment of the present invention, the precursor web is subjected to pre-entangling on a foraminous-forming surface prior to juxtaposition of a support layer or scrim and subsequent three-dimensional imaging. Alternately, one or more layers of fibrous matrix are juxtaposed with one or more support layers or scrims, then the layered construct is pre-entangled to form a precursor web which is imaged directly, or subjected to further fiber, filament, support layers, or scrim layers prior to imaging.
The present method further contemplates the provision of a three-dimensional image transfer device having a movable imaging surface. In a typical configuration, the image transfer device may comprise a drum-like apparatus, which is rotatable with respect to one or more hydroentangling manifolds.
The precursor web is advanced onto the imaging surface of the image transfer device. Hydroentanglement of the precursor web is effected to form a three-dimensionally imaged fabric. Significantly, the incorporation of at least one support layer or scrim acts to focus the fabric tension therein, allowing for improved imaging of the staple fiber layer or layers, and resulting in a more pronounced three-dimensional image.
Subsequent to hydroentanglement, the three-dimensionally imaged fabric may be subjected to one or more variety of post-entanglement treatments. Such treatments may include application of a polymeric binder composition, mechanical compacting, application of surfactant or electrostatic compositions, and like processes.
A further aspect of the present invention is directed to a method of forming a durable nonwoven fabric, which exhibits a pronounced three-dimensionality, while providing the necessary resistance to abrasion and elongation, to facilitate use in a wide variety of applications. The fabric exhibits a high degree of fiber retention, thus permitting its use in those applications in which the fabric is used as a home cleaning substrate or medical fabric. Further, the support layer or scrim aids in preventing the distortion of the imprinted image upon the application of tension to the composite fabric during routine processing and use.
A method of making the present durable nonwoven fabric comprises the steps of providing a precursor web, which is subjected to hydroentangling. The precursor web is formed into a three-dimensionally imaged nonwoven fabric by hydroentanglement on a three-dimensional image transfer device. The image transfer device defines three-dimensional elements against which the precursor web is forced during hydroentanglement, whereby the fibrous constituents of the web are imaged by movement into regions between the three-dimensional elements and surface asperities of the image transfer device.
In the preferred form, the precursor web is hydroentangled on a foraminous surface prior to hydroentangling on the image transfer device. This pre-entangling of the precursor web acts to integrate the fibrous components of the web, but does not impart a three-dimensional image as can be achieved through the use of the three-dimensional image transfer device.
Optionally, subsequent to three-dimensional imaging, the imaged nonwoven fabric can be treated with a performance or aesthetic modifying composition to further alter the fabric structure or to meet end-use article requirements. A polymeric binder composition can be selected to enhance durability characteristics of the fabric, while maintaining the desired softness and drapeability of the three-dimensionally imaged fabric. A surfactant can be applied so as to impart hydrophilic properties. In addition, electrostatic modifying compound can be used to aid in cleaning or dusting applications.
Other features and advantages of the present invention will become readily apparent from the following detailed description, the accompanying drawings, and the appended claims.